Device and methods for plasma sterilization

ABSTRACT

The invention provides methods and apparatus for sterilizing articles. According to one exemplary method, at least one article is placed into a chamber and a vacuum is applied to the chamber. After the pressure within the chamber is sufficiently reduced, water vapor is introduced into the chamber and electromagnetic radiation energy is applied to produce a plasma. In one particularly preferable aspect, the chamber is allowed to reach a static condition before the water vapor is introduced. In this way, the water vapor is able to equally distribute itself throughout the volume of the chamber so that an equally distributed plasma can be produced upon application of the electromagnetic radiation energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to methods and apparatus forsterilizing articles, and in particular to methods and apparatus forsterilizing articles with a gas plasma generated from a gas mixture ofoxidizing and reducing agents. In one particular aspect, this inventionprovides for the sterilization of articles with a gas plasma generatedfrom water vapor.

A variety of sterilization methods have been proposed for sterilizing awide range of articles such as medical products, surgical instruments,pharmaceutical products, and the like. One common method is bysubjecting the articles to a gas such as ethylene oxide or otherdisinfecting gases. Irradiation procedures have also been proposed forsterilizing articles such as medical products.

One expectation for all sterilizing procedures is that they musteffectively kill all organisms without damage to the articles or goodsbeing sterilized. Although some sterilization procedures meet thesecriteria, including the use of ethylene oxide and other procedures, manysterilizers using such gases suffer from number of serious drawbacks.For example, use of such gases is often too corrosive for the articlesbeing sterilized or their packaging materials. Another drawback is thata toxic residue usually remains on the sterilized articles. In anotherdrawback that affects all traditional methods of sterilization, althoughthe microorganisms are usually destroyed by the plasma, the destroyedmicroorganisms still physically remain on the articles.

Sterilization gas procedures and irradiation procedures often exposeworkers and the environment to unacceptable safety standards. Suchexposure is becoming increasingly more undesirable, particularly inlight of state and federal legislation restricting the use of hazardousmaterials.

Such restrictions are forcing hospitals and other medical facilities tosearch for other alternatives. One such alternative is a plasmasterilizer. Plasma sterilizers operate by injecting a gas into a chamberand applying electromagnetic radiation energy to the gas in the chamberwhich in turn ionizes the body of gas. The ionized gas should be highlyreactive and reacts with microorganisms on the surface of the articlesto be sterilized. The reactions between the ionized gas and themicroorganisms should effectively destroy the microorganisms.Sterilizing plasmas have been generated with a wide variety of gases asset forth generally in U.S. Pat. No. 5,184,046, the disclosure of whichis herein incorporated by reference.

One drawback with using such plasma sterilizers is that it is oftendifficult to ensure that all of the articles in the sterilizer have beencompletely sterilized. Such a problem arises because of the difficultyin achieving uniform gas dynamics and uniform plasma density when thearticles being sterilized are of different sizes or shapes. This problemis compounded by the use of non-cylindrical reaction chambers anddiffering batch sizes. The non-uniformity of the gas dynamics results ina non-uniform plasma density, which in turn provides a non-uniformplasma treatment and insufficient sterilization.

Another problem experienced in sterilizing articles is the problem ofmaintaining the sterility of the articles during packaging. Currentsterilization techniques, such as plasma sterilization and gassterilization, generally require the articles to be sterilized and thensubsequently packaged. To maintain sterility during packaging, thearticles are packaged in a sterile environment. Such a procedure isinconvenient and expensive.

It would therefore be desirable to provide methods and apparatus toovercome or reduce such problems. In particular, the methods andapparatus should provide for plasma sterilization that is not corrosiveto the articles and does not leave toxic residues on the articles. Themethods and apparatus should not only be able to effectively destroy themicroorganisms, but also to remove them from the articles. Further, themethods and apparatus should provide for uniform plasma distribution,thereby insuring uniform sterilization regardless of the chambergeometry or the size and geometry of the articles to be sterilized. Itwould further be desirable to provide methods and apparatus forsterilizing articles within packaging suitable for delivery to an enduser.

2. Description of the Background Art

U.S. Pat. Nos. 5,115,166, 5,184,046, and 5,325,020 describe variousapparatus and methods for plasma sterilization.

U.S. Pat. No. 4,207,286 describes a sterilization method using acontinuous flow, low pressure gas plasma.

SUMMARY OF THE INVENTION

The invention provides methods and apparatus for sterilizing articlesusing a gas plasma. According to one particular method, an article isplaced into a sterilization chamber and a vacuum is applied to thechamber to reduce the pressure within the chamber. With the pressurereduced, water vapor is introduced into the chamber. The water vapor canbe introduced alone or can optionally be introduced with a carrier gas.With the water vapor in the chamber, an electromagnetic radiation energyis applied to the chamber to produce a plasma. The electromagneticradiation energy excites the water molecules and causes them todisassociate thereby creating reactive radicals. The reactive radicalsvaporize and combine with the by-products of the spores and othermicroorganisms and to effectively destroy and remove the spores andother microorganisms from the articles, thereby sterilizing thearticles.

In an exemplary aspect, the carrier gas comprises air. Alternatively,the carrier gas can be a gas selected from the group consisting ofargon, hydrogen, oxygen, nitrogen, helium, nitrogen tri-fluoride, andnitrous oxide. The electromagnetic radiation energy applied to thechamber is preferably in the range from about 5 KHz to 10 GHz, and morepreferably at about 2.45 GHz. Such a wavelength is preferable because ofits effectiveness in disassociating the hydrogen and oxygen atoms of thewater vapor.

When the water vapor is introduced into the chamber, the pressure withinthe chamber is preferably within the range from about 100 mTorr to 10Torr. In another aspect, the temperature within the chamber ispreferably in the range from about 25° C. to 100° C.

In an alternative method for sterilizing articles, at least one articleis placed into a sterilization chamber and a vacuum is applied to thechamber until a predetermined pressure is reached within the chamber.Once such a pressure is reached, application of the vacuum is ceased anda static condition is allowed to develop within the chamber. Once astatic condition has been reached, an amount of gas is introduced intothe chamber and is allowed to uniformly distribute throughout thechamber. Because of the static condition within the chamber, pressure isequal throughout the chamber allowing the concentration of the gas toreadily become uniform throughout the entire volume of the chamber. Insuch a state, electromagnetic radiation energy is applied to the chamberto produce a plasma.

After the plasma has had sufficient time to react with the spores andother microorganisms, the electromagnetic radiation power is ceased andany gases are exhausted from the chamber. One or more cycles can beapplied. In a preferable aspect, the gas introduced into the chamber iswater vapor. When water vapor is used to produce the plasma, thereactions within the chamber produce water vapor, oxygen, and nitrogenwith small amounts of carbon dioxide and carbon monoxide. Such gases canbe safely exhausted into the atmosphere.

After the gases are exhausted into the atmosphere, the cycle of applyinga vacuum to the chamber, allowing a static condition to develop,introducing the gas into the chamber, and applying electromagneticradiation energy are again repeated as necessary to ensure that thearticles within the chamber are sufficiently sterilized.

The invention provides an apparatus for sterilizing articles whichincludes a sterilization chamber and both a vacuum pump and a gas sourcein communication with the chamber. The vacuum pump allows the pressurewithin the chamber to be reduced. Once the pressure is reduced, the gassource can be employed to introduce a gas into the chamber. Theapparatus further includes an electromagnetic radiation energy source toproduce a plasma from the gas within the chamber. A controller isprovided for cyclically actuating the vacuum pump, the gas source, andthe electromagnetic radiation energy source. In a preferable aspect, thecontroller is configured so that the vacuum pump, the gas source, andthe electromagnetic radiation energy source are actuated at separatetimes. In this way, the apparatus can be operated in a cyclical mannerto continuously produce and exhaust a plasma. Operation in this mannerallows the articles to be uniformly sterilized. In particular, thecontroller allows the vacuum pump to reduce the pressure in the chamberto a desired pressure. At this point, the controller stops the vacuumpump and allows the chamber to reach a static condition. When such acondition is reached, the controller actuates the gas source to injectan amount of gas into the chamber. Since the chamber is in a staticcondition, the gas equally distributes throughout the chamber. At thispoint, the electromagnetic radiation energy source is actuated by thecontroller to produce a uniformly distributed plasma within the chamberfor uniformly sterilizing the articles. After reaction of the plasmawith the microorganisms on the articles, the resulting gases areexhausted and the controller sends a signal to repeat the cycle as oftenas is desired.

In a preferable aspect, the vacuum pump is connected to thesterilization chamber by a tube, and the controller includes a rotatabledisk having an orifice that can be aligned with the tube as the disk isrotated. In this manner, each time the orifice comes in alignment withthe tube, a vacuum is created within the chamber. The rotating disk alsoserves as a timer to actuate the injection of the gas and theapplication of the electromagnetic radiation energy. A sensor can beemployed for sensing the degree of rotation of the disk so that a signalcan be sent to actuate the gas source or the electromagnetic radiationenergy source at the appropriate times. In this way, the cycle of thesterilizer is controlled by the rotation of the disk.

The invention further provides a method an apparatus for sterilizingpre-packaged articles, with the packaging being suitable for delivery toan end user. The packaging includes a container constructed of amaterial transparent to electromagnetic radiation energy, such asplastic. To sterilize the article, the article is placed in thecontainer and a vacuum is applied to the chamber until a pressure in therange from about 1 mTorr to 100 mTorr is reached. The container is thenback filled with water vapor to a pressure in the range from about 100mTorr to 100 Torr. A carrier gas is used to introduce the water vapor.The container is then sealed and is subjected to electromagneticradiation energy to form a highly energetic water vapor in thecontainer. The electromagnetic radiation is then ceased and a staticcondition is allowed to develop in the container. The electromagneticradiation energy is again reapplied until sterilization is complete. Thearticles then remain in a sterilized environment within the packaginguntil removed by the end user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating an exemplary method for sterilizingarticles using a gas plasma according to the present invention.

FIG. 2 illustrates a partially cut-away side view of a sterilizationapparatus according to the present invention.

FIG. 3 illustrates a top view of a rotating chopper valve forcontrolling the sterilization cycle of the apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

This invention provides methods and apparatus for sterilizing articles,particularly by the use of a gas plasma generated from a gas mixture ofoxidizing and reducing agents. In a preferable aspect, the articles aresterilized with a gas plasma that is generated from water vapor.

According to the method for sterilizing articles using a gas plasma thatis created from water vapor, at least one article is introduced into asterilization chamber. The article can be selected from any of a numberof articles, such as surgical instruments, dental instruments, medicalproducts, pharmaceutical products, and the like. After the article iswithin the chamber, a vacuum is applied to the chamber to reduce thepressure within the chamber to a pressure below atmospheric pressure.Preferably, the pressure will be reduced until it is in the range fromabout 100 mTorr to 10 Torr. When the pressure within the chamber iswithin the desired range, a water vapor is introduced into the chamber.Conveniently, the water vapor can be introduced into the chamber by acarrier gas. The carrier gas can be any one of a number of gasesincluding such gases as air, argon, hydrogen, nitrogen, oxygen, helium,nitrogen tri-fluoride, nitrous-oxide, and the like, or any mixturesthereof. Preferably, air will be used as the carrier gas. Although suchcarrier gases can conveniently be used to assist in introducing thewater vapor into the chamber, a novel feature of the invention is thatwater vapor alone can be used to produce the plasma.

Once the water vapor has been introduced into the chamber,electromagnetic radiation energy is applied to the water vapor while thepressure within the chamber is maintained in the desired range.Electromagnetic radiation energy as used herein includes all radiofrequency energy and particularly any radio frequency energy having awavelength in the range from about 5 KHz to 10 GHz, and also includesenergy such as microwave, infrared light, visible light, ultravioletlight, laser, X-ray energy and gamma radiation. When the radio frequencyenergy is supplied, the water molecules are driven into a high energystate, causing the molecules to disassociate into reactive radicals andforming a plasma. The radio frequency energy will preferably be at about2.45 GHz which has proven to be effective in fractionating the watermolecules. The reactive radicals then vaporize and combine with theby-products of spores or other microorganisms on the articles tosterilize the articles. The reactions of the radicals with the sporesand other microorganisms produce water vapor, oxygen, nitrogen, andsmall amounts of carbon dioxide and carbon monoxide. A particularadvantage in using water vapor to create the plasma is that when thereactive radicals combine with the spores and other microorganisms onthe articles, they are effectively vaporized. In this way, the sporesand other microorganisms are physically removed from the articles andconverted to gas form which is then exhausted from the chamber. Afurther advantage in using water vapor to create the plasma is that theexhausted gases, i.e., water vapor, oxygen, nitrogen, and small amountsof carbon dioxide and carbon monoxide, can be safely exhausted into theatmosphere. In still a further advantage, the temperature within thechamber during the sterilization process can be in the range from about25° C. to 100° C. Such temperatures provide for a safe workingenvironment and do not impose additional costs in constructing thesterilization apparatus.

The invention further provides a method for uniformly sterilizingarticles using a gas plasma. The method is set forth in the flow chartof FIG. 1. According to the method, at least one article is placed intoa sterilization chamber. The article can be of any size or geometry aslong as it can fit within the sterilization chamber. With the article inthe chamber, a vacuum is applied to the chamber to reduce the pressureto a predetermined amount. When such a pressure is reached, applicationof the vacuum is ceased and a static condition is allowed to develop inthe chamber, i.e., a condition where the pressure remains essentiallyconstant and equal throughout the entire interior of the chamber. Once astatic condition has been reached, a discrete amount of gas isintroduced into the chamber. Because of the static condition within thechamber, the gas rapidly distributes itself uniformly throughout theentire volume of the chamber as dictated by Boyle's law. This removesgas flow dynamics from the equation.

With the gas equally distributed throughout the entire interior volumeof the chamber, electromagnetic radiation, and preferably radiofrequency energy, is applied to the gas to produce a plasma. The gas canbe any one of a number of gases capable of producing reactive radicals,but will preferably include water vapor. The radio frequency energy isapplied for a time sufficient to allow the reactive radicals to reactwith the spores and other microorganisms on the articles. The amount oftime the radio frequency energy is applied can be increased as desiredto introduce a safety factor. After the plasma has had sufficient timeto react, the radio frequency energy is ceased and the resultant gasesare exhausted from the chamber.

Because only a discrete amount of gas is introduced at a time into thechamber, the cycle of applying a vacuum to the chamber, allowing astatic condition to develop, introducing another amount of gas into thechamber, and applying radio frequency energy can again be repeated asnecessary to ensure that the articles within the chamber aresufficiently sterilized.

Referring to FIG. 2, an exemplary embodiment of an apparatus 6 forsterilizing articles will be described. The apparatus 6 is convenientlyplaced on a table 8 for easier access. The apparatus 6 includes a viewport 10 within a door 12. The door 12 is connected to a reaction chamber14 via a flange 15. Visual access to the reaction chamber 14 is obtainedthrough the view port 10, while physical access is gained by opening thedoor 12. Preferably, the door 12 will be hingedly connected to theflange 15. The door 12, the flange 15, and the chamber 14 willpreferably all be constructed of stainless steel. Use of stainless steelfor these components is advantageous because the stainless steel doesnot sputter (i.e., the physical deposition of material on substrates) aswould aluminum or aluminum oxide, causing damage and contamination tothe articles being sterilized.

Attached to an opposite end of the reaction chamber 14 is anotherstainless steel flange 38. The flange 38 is used to attach a materialtransparent to radio frequency energy, such as a glass or quartz plateseal 20 through which radio frequency energy is directed.

To inject gas into the reaction chamber 14, a gas injection port 24 isprovided. Gas is supplied to the injection port 24 through a gas line26. In turn, the gas line 26 is in communication with a gas source 28.The gas source 28 can be configured to provide any one of a variety ofgases, and will preferably be configured to provide water vapor as thegas. To provide the water vapor, the gas source 28 includes a container30 having an amount of water H₂ O. Placed in the water is a carrier gasdelivery tube 32 for bubbling a carrier gas through the water. In thisway, as the carrier gas is bubbled through the water, water vapor isproduced which can be delivered to the reaction chamber 14 through thegas line 26. A gas injection valve 34 is provided for controllinginjection of the gas into the reaction chamber 14. A gas metering valve36 is provided to meter the amount of gas travelling through the gasline 26.

Although shown with only a single gas injection port 24, the apparatus 6can alternatively be provided with a plurality of gas injection portsdisposed throughout the reaction chamber 14. In such a configuration, aheader can be provided to distribute the gas to the various gasinjection ports around the reaction chamber 14.

A radio frequency energy source 22 is provided for supplying radiofrequency energy into the chamber at a wavelength in the range fromabout 5 KHz to 10 GHz. Preferably, the radio frequency energy suppliedby the generator source 22 will be at about 2.45 GHz. Such a wavelengthis the same wavelength produced by most commercially available microwaveovens. Conveniently, the generator source 22 can be constructed from thepower supply of a commercially available microwave oven. The radiofrequency energy is directed through the plate seal 20 and into thereaction chamber 14. As previously described, the plate seal 20 isconstructed of a material transparent to radio frequency energy, and ispreferably constructed of a glass or a quartz plate. The stainless steelflange 38 is provided to attach to the generator source 22 to thereaction chamber 14.

The gas injected into the reaction chamber 14 is allowed to equallydistribute itself throughout the entire interior volume of the reactionchamber 14. This is accomplished by sealing the chamber 14 after the gasis injected. When the gas is within the reaction chamber 14, the radiofrequency generator source 22 can be actuated to direct energy throughthe plate seal 20 and into the reaction chamber 14. In this way, aplasma is produced when the gas is energized by the radio frequencyenergy.

In some instances, it may be desirable to provide a diffuser plate 18.The diffuser plate 18 is held by a flange 16 and divides the reactionchamber 14 into two separate volumes. The volume adjacent the door 12(volume A) is for holding the articles and the volume adjacent thegenerator source 22 (volume B) is for receiving the injected gas. Thediffuser plate 18 contains at least one through hole so that the twovolumes A, B can communicate. More than one through hole can be includedfor multiple point injection of the gas. As gas is injected into volumeB adjacent the radio frequency generator source 22, this volume isimmediately filled with gas. Volume A is also almost immediately filledwith the gas through the through hole. The rate at which volume A isfilled can be varied depending on the pressure difference between thevolumes A, B and the size and quantity of through holes.

At this point, it is possible to produce a plasma in volume B, but notin volume A. As described hereinafter, plasma can alternatively beproduced in both volume A and B in any proportion so that the articlesin volume A can be exposed only to the reactive gases, or to anycombination of reactive gases and ionic bombardment. To produce theplasma only in volume B, a metallic cover is placed adjacent the plate18 (or substituted for plate 18) to prevent radiation energy fromentering volume A when the radio frequency generator 22 is actuated toproduce a plasma in volume B. In this way, the articles in volume Areceive no ionic bombardment and are only exposed to the previouslydiffused reactive gases in volume A. This procedure is particularlybeneficial when sterilizing sensitive articles such as cameras,microscopes, optics, implantable sensors, lenses, and the like.

To sterilize without ionic bombardment over a broader range ofparameters, a second metal gas diffusion plate with one or more throughholes can be rotatably received relative to the first plate. As thesecond plate is rotated relative to the first plate, the through holescome in and out of alignment allowing for varying degrees of gasdiffusion into volume A.

The radio frequency generator source 22 can be actuated at differenttimes relative to the injection of the gas into the volume B to vary theamount of plasma diffused into the volume A. If the radio frequencyenergy is actuated just as the gas is injected into the volume B, then aplasma will be created that can then be diffused into the volume A. Ifthe generator source 22 is actuated well after the gas has diffused intothe volume A, then virtually no plasma will be diffused into the volumeA.

In some circumstances, particularly when using low frequencyelectromagnetic radiation energy, it may be difficult to couple theelectromagnetic radiation energy through the plate seal 20. In such acase, the electromagnetic radiation energy can be inductively orcapacity coupled through the glass or quartz plate 20 into the reactionchamber. To capacity couple the energy source, an electrode can beemployed and placed either inside or outside the reaction chamber 14.Use of the electrode inside the chamber 14 is useful when usingelectromagnetic radiation energy having a frequency of 10 MHz or less.Use of the electrodes outside the chamber is useful when usingelectromagnetic radiation energy having frequencies in the range from 10MHz to 900 MHz. To inductively couple, a copper tube, preferably havinga diameter in the range from 3/16" to 1/4" is arranged on the outsidesurface of the plate 20. Energy is supplied through the wire at afrequency in the range of about 10 MHz to 900 MHz and is coupled throughthe plate 20 to produce the plasma.

The reaction chamber 14 can be constructed of any geometry, but willpreferably be orthogonal or cylindrical in geometry. An orthogonalgeometry is advantageous when using trays to carry the articles to besterilized. Use of trays allows for easy arrangement of the articleswithin the chamber 14.

To reduce the pressure within the reaction chamber 14 prior to injectionof the gas, a vacuum pump 40 is provided. The vacuum pump 40 can be anypump capable of reducing pressures within the reaction chamber 14 up toa pressure of about 10 mTorr. An exemplary vacuum pump 40 is one such asthe Alcatel 1220, commercially available from Alcatel. The vacuum pump40 also serves to exhaust gases from the reaction chamber 14 aftersterilization has occurred. The vacuum pump 40 communicates with thereaction chamber 14 via an exhaust port 42.

As previously described in the method of the invention, it is desirableto provide a uniformly distributed plasma within the chamber 14regardless of the geometry of the reaction chamber 14 or the articlesthemselves. To provide a uniform plasma treatment, a static condition iscreated within the chamber 14 by ceasing the pumping. A discrete amountof gas can be injected into the reaction chamber 14 through the port 24which is then closed. The gas is then allowed to equally distributeitself throughout the entire interior volume of the reaction chamber 14.Radio frequency energy from the generator source 22 is directed into thechamber 14 to create a uniform plasma, thereby allowing for uniformsterilization of the articles regardless of their geometry. Thesterilizing procedure is accomplished with one or more sterilizationcycles.

In order to insure sufficient sterilization when providing such atreatment where only a discrete amount of gas is introduced, theapparatus 6 includes a controller for controlling a repeatingsterilization cycle. The controller separately and repeatedly actuatesthe vacuum, the gas injection, the radio frequency energy, and theexhausting of spent gases. In this way, the articles within thesterilization chamber are continually subjected to a series of uniformlydistributed gas plasma.

The controller can be any controller capable of separately actuating thevacuum pump 40, the gas injection valve 34, actuation of the generatorsource 22, and the exhaustion of gases through the exhaust port 42 in asystematic and controlled manner. An exemplary controller forcontrolling a sterilization cycle as just described is illustrated inFIGS. 2 and 3. The controller includes a rotating chopper valve 44 thatis rotated by a chopper valve drive motor 46. A top view of the choppervalve 44 is shown in FIG. 3. The chopper valve 44 includes an orifice 46that 20 is alignable with the exhaust port 42. As the chopper valve 44rotates, the orifice 46 passes in and out of alignment with exhaust port42. The vacuum pump 40 is continuously actuated so that a vacuum will beapplied to the reaction chamber 14 as the orifice 46 becomes alignedwith the exhaust port 42. Disposed on the chopper valve 44 are a seriesof indicators which can be sensed by a sensor, such as an optical sensor(not shown), and used to actuate the gas injection valve 34 and thegenerator source 22. A gas injection indicator 48 is provided foractuating the valve 34 to inject a gas through the gas injection port24. Spaced-apart from the gas injection indicator 48 is a radiofrequency "on" indicator 50. As the radio frequency "on" indicatorpasses the sensor, a signal is sent to actuate the radio frequencygenerator source 22. The radio frequency energy source 22 remainsactuated until the sensor senses a radio frequency "off" indicator 52.

The sensor will preferably be connected to a microprocessor or othercontroller for sending signals to actuate the generator source 22 andthe gas injection valve 34 so that gas can be injected and radiofrequency energy can be applied at the appropriate times.

In this way, the chopper valve 44 acts as an event timer which controlsa sterilization cycle capable of producing a series of uniformlydistributed plasma treatments within the reaction chamber 14, regardlessof its geometry. As the chopper valve 44 rotates, the orifice 46 comesinto alignment with the exhaust port 42 thereby creating a vacuum withinthe chamber 14. As the orifice 46 passes out of alignment, the vacuum isstopped and a static condition is allowed to develop within the chamber14. At this point, the sensor senses the gas injector indicator 48 whichsends a signal to open the valve 34 and to inject gas into the reactionchamber 14 through the gas injection port 24. Because of the staticcondition within the chamber 14, the gas uniformly distributes itselfthroughout the reaction chamber 14. The sensor then senses the radiofrequency "on" indicator and a signal is sent to the radio frequencygenerator source 22 to apply radio frequency energy to the gas and toproduce a uniformly distributed gas plasma which reacts with themicroorganisms on the articles. The sensor then senses the radiofrequency "off" indicator 52 and sends a signal to cease application ofthe radio frequency energy. The orifice 46 then comes back intoalignment with the exhaust port 42 to exhaust the spent gases and toagain create a vacuum within the chamber 14. The cycle is then repeatedas often as necessary until the sterilization procedure is complete. Therepetition rate of the cycle is a function of the rotational speed ofthe chopper valve 44, and the duration of any given event in the cycleis a function of the placement of the indicators 48-52 on the choppervalve 44. Preferably, the cycle will be repeatable up to about 100cycles per minute. Although the controller for controlling thesterilization cycle of the apparatus 6 has been described in connectionwith the chopper valve 44, any controller capable of separatelyactuating the events in the cycle can be employed. For example, apersonal computer could be configured to sequentially actuate the pump44, the injection valve 34, and the generator source 22.

The invention further provides a method and apparatus for sterilizingarticles that are prepackaged in a container. When articles aremanufactured, it is desirable to deliver them to the end user in asterile protective package. This may require sterilizing the articlesand then packaging them in a sterile environment. This inventioneliminates such a procedure by sterilizing the articles while withintheir packaging materials. To sterilize the articles in this manner, theinvention employs a packaging container for prepackaging the articles.The container is constructed of a material transparent toelectromagnetic radiation frequency energy, such as plastic. Thearticles are placed in the container, and before the container is sealedthe container is pumped to a vacuum of about 1 mTorr to 100 mTorr. Thecontainer is then back-filled with water vapor to a pressure of about100 mTorr to 100 Torr. To back-fill the water vapor, a carrier gas isemployed. The carrier gas is preferably air, but other gases can beemployed such as argon, hydrogen, nitrogen, oxygen, helium, nitrogentri-fluoride, nitrous oxide or mixtures thereof.

The prepackaged articles are then sterilized by placing the container inclose proximity to an electromagnetic radiation source. The energysource is activated for a predetermined time to form a highly energeticwater vapor. The electromagnetic radiation energy is then ceased for apredetermined time so that a static condition can develop within thecontainer. This allows the pressure to become equalized and theconcentration of the gases to become uniform throughout the volume ofthe container. The electromagnetic radiation energy is then reactivatedto produce a uniformly distributed plasma. The energy source remains onfor a predetermined time and the cycle may be repeated as many times asneeded to complete the sterilization process. During the process thereactive radicals in the plasma vaporize and combine with theby-products of spores or other microorganisms on the articles. Thisproduces water vapor, oxygen, nitrogen, and small amounts of carbondioxide and carbon monoxide which all remain in the package untilopened. However, the combination of these gases is inert and can besafely exhausted into the atmosphere when the containers are opened. 5In this way, the articles in the container remain sterilized until theyare removed for use.

Although the foregoing invention has been described in detail by way ofillustration and example, for purposes of clarity of understanding, itwill be obvious that certain changes and modifications may be practicedwithin the scope of the appended claims.

What is claimed is:
 1. A method for sterilizing articles,comprising:placing at least one article into a chamber; applying avacuum to the chamber; ceasing application of the vacuum and allowing astatic condition to develop within the chamber where the pressurethroughout the chamber is essentially equal and constant; after thestatic condition has developed, introducing an amount of water vaporinto the chamber and allowing the water vapor to uniformly distributewithin the chamber; and applying electromagnetic radiation energy to thechamber after the water vapor has become uniformly distributed withinthe chamber to produce a substantially uniformly distributed plasmawithin the chamber.
 2. The method of claim 1, wherein the water vapor isintroduced into the chamber with a carrier gas.
 3. The method of claim2, wherein the carrier gas is air.
 4. The method of claim 2, wherein thecarrier gas is selected from the group consisting of argon, oxygen,nitrogen, helium, nitrous oxide and nitrogen tri-fluoride.
 5. The methodof claim 1, wherein the electromagnetic radiation energy is in the rangefrom about 5 KHz to 10 GHz.
 6. The method of claim 1, wherein theelectromagnetic radiation energy is about 2.45 GHz.
 7. The method ofclaim 1, wherein the pressure within the chamber when the water vapor isintroduced is in the range from about 0.01 Torr to 100 Torr, and whereinthe temperature within the chamber is in the range from about 25° C. to100° C.
 8. The method of claim 1, wherein the chamber is a packagingcontainer, and wherein the electromagnetic radiation energy is ceasedand is subsequently applied a second time.
 9. A method for sterilizingarticles, comprising:(a) placing at least one article into a chamber;(b) applying a vacuum to the chamber until a predetermined pressure isreached within the chamber; (c) ceasing application of the vacuum andallowing a static condition to develop in the chamber where the pressurethroughout the chamber is essentially equal and constant; (d) after thestatic condition has developed, introducing an amount of gas into thechamber and allowing the gas to uniformly distribute throughout thechamber; and (e) applying electromagnetic radiation energy to thechamber after the gas has become uniformly distributed within thechamber to produce a substantially uniformly distributed plasma withinthe chamber.
 10. The method of claim 9, further comprising:(f) ceasingapplication of the electromagnetic radiation energy; (g) exhaustinggases from the chamber; and (h) repeating the steps (b) through (g). 11.The method of claim 9, wherein the gas comprises water vapor.
 12. Themethod of claim 11, wherein the water vapor is introduced into thechamber with a carrier gas.
 13. The method of claim 12, wherein thecarrier gas is air.
 14. The method of claim 9, wherein theelectromagnetic radiation energy is in the range from about 5 KHz to 10GHz.
 15. A method for sterilizing articles, comprising:placing at leastone article into a chamber; applying a vacuum to the chamber;introducing only water vapor into the chamber ceasing application of thevacuum and allowing a static condition to develop in the chamber wherethe pressure throughout the chamber is essentially equal and constant;and applying electromagnetic radiation energy to the chamber after thewater vapor has become uniformly distributed within the chamber toproduce a substantially uniformly distributed plasma within the chamberto produce a substantially uniformly distributed plasma within thechamber.
 16. A method for sterilizing articles, comprising:placing atleast one article into a container; applying a vacuum to the container;introducing water vapor into the container and sealing the containerwhile a vacuum condition exists within the container so that the watervapor is maintained at the vacuum condition; placing the container intoa chamber after the water vapor has been sealed within the container;applying electromagnetic radiation energy to the chamber to produce asubstantially uniformly distributed plasma within the container.
 17. Amethod as in claim 16, wherein the container has a pressure in the rangefrom about 100 mTorr to about 100 Torr when sealed.
 18. A method as inclaim 16, further comprising ceasing application of the electromagneticradiation energy and waiting a predetermined amount of time until astatic condition develops within the container.
 19. A method as in claim18, further comprising reapplying the electromagnetic radiation energyafter the static condition has developed.